The present invention relates to processes for depositing metals and/or metal oxides on substrates and to substrates having metal and/or metal oxide coatings produced by such processes.
Processes used to deposit coatings on substrate surfaces find use in many fields. Methods used to deposit coatings include physical vapour deposition methods such as pulsed laser deposition (PLD) and sputtering or solution based methods such as spray pyrolysis and sol-gel.
US-A-2012/168,747 discloses methods for forming a mixed (e.g. InGaZnO, InZnO or HfInZnO) oxide semiconductor as a thin film and electronic devices including the oxide film using liquid coating methods and subsequent annealing.
US-A-2010/0251,936 discloses a method of fabricating a liquid, especially by sol gel methods, for an oxide thin film for display and electronic devices which includes mixing at least two kinds of dispersoids selected from zinc, indium, gallium, tin or thallium compounds.
One useful method is chemical vapour deposition (CVD) wherein a fluid precursor is delivered to the surface of the substrate in order to deposit the coating. Particular types of CVD include metal organic (MO) CVD, combustion (C) CVD, plasma enhanced (PE) CVD and aerosol-assisted (AA) CVD.
US-A-2008/241,423 relates to formation of non-native films on surfaces of compound semiconductor films, and more particularly relates to the preparation of III-V semiconductor surfaces for deposition and the subsequent deposition of a film by the Atomic Layer Deposition (ALD) method. The methods described involve exposing a III-V semiconductor surface to a triflating or trifluoroacetylating agent to terminate the III-V semiconductor surface with triflate or trifluoroacetate groups.
Tao et al. (Dalton Trans. 2011, 40, p. 9250) disclose disilver methanedisulphonate phosphorus complexes and hot wall MOCVD on oxidised silicon substrates at 395° C. to 450° C.
EP-A-2 065 364 discloses metal containing tridentate β-ketoiminates as metal containing precursors for chemical vapour deposition processes including atomic layer deposition for fabricating conformal metal containing films on substrates such as silicon for use in semiconductor fabrication.
CVD processes have found use in modifying the light transmission, conductive and other properties of e.g. glass. Useful coatings for, in particular, glass substrates, are coatings of metals and/or metal oxide including transparent conductive oxides (TCO). TCO coatings are useful, for example, as transparent electrodes in flat panel displays, solar cells and organic light emitting diodes and as low emissivity coatings on glazings. TCO coating materials include indium tin oxide (ITO), F-doped tin oxide and zinc oxide.
Zinc oxide is a semiconductor material with a direct wide band gap. Thin films of nominally undoped ZnO exhibit n-type conductivity. The conductivity of zinc oxide can be increased by doping with an extrinsic dopant source, such as Al or Ga. An important aspect of successful CVD processes is the precursor. In the case of zinc oxide coatings, a number of zinc precursors have been investigated, with diethyl zinc often being used. Diethyl zinc is volatile and therefore generally suitable for many CVD techniques. Unfortunately, use of diethyl zinc can be problematic because it is reactive.
WO-A-2013/136052 discloses a chemical vapour deposition process using a gaseous mixture containing an alkyl zinc compound and gaseous inorganic oxygen-containing compounds.
US-A-2012/240,634 discloses a CVD process to produce inter alia Ga-doped ZnO using a gaseous zinc-containing compound (e.g. an alkyl zinc compound), an oxygen-containing compound, and an acetonate compound.